Railway Signalling

RAILWAY SIGNALLING Railway Signalling has passed through a long period of de velopment and is to-day an efficient means for safeguarding and expediting the movement of railway trains. This article traces this development from a crude type of fixed signal in use in the early days of railways to the perfected systems of to-day.

Fixed Signals

are signals of fixed location used to govern trains by displaying aspects whose indications show when, where and how to go and when and where to stop. The principal types of fixed signals as follows: Crossbar-and-lamp Signal, England, 1834; the first fixed rail way signal. Ball Signal, England, 1837; type once used in the United States as a railway crossing signal. Semaphore Signal, England, 1841; this type, in general use to-day, was an adaptation to railway use of the Chappe semaphore, 1793, used in optical telegraphy. Banner Box Signal, United States, 1863 ; early type of manual block signal. "Smas/iboard" Drawbridge Signal, United States, 1868. In stop position the red board was lowered so as to strike the locomotive stack should the signal be overrun. "Banjo" Signal, United States, 1871, type of first electrically operated auto matic block signal. Clockwork Signal, United States, 1879, me chanically operated automatic block signal with electric control.

Semaphore Signals: Electro-pneumatic type, United States, 1881, the first power operated semaphore ; Electric type, United States, 1893, the forerunner of present day electric motor semaphore signals ; Upper Quadrant type, United States, 1908, for both manual and power operation (Pl. IV., fig. I). Previous types operated in lower quadrant. Light Signals displaying coloured electric lights for both day and night indications : Colour Light type, United States, 1908 (Pl. IV., fig. 2) ; Position Light type, United States, 1915 (P1. IV., fig. 3) ; Colour-position Light type, United States, 1921 (Pl. IV., fig. 4).

Train Dispatching

in the United States is a highly developed method of directing train movement by the use of general rules, time-tables (with special instructions), train orders, or by signals in place of written train orders.

Rules and time-tables are the plans for directing train move ment. Train orders are to meet conditions which cannot always be anticipated. If train operation could be conducted by time tables without delay, train orders would not be necessary. Such precision being impossible, train orders are used to supplement the time-table.

Train dispatching has reached the third stage of its develop ment. The first, when the time-table was the sole authority for train movement, was the "time-table" stage. The second or "train order" stage began in 1851 when the electric telegraph was first used for sending train orders. The written train order is now being superseded by the unmistakable indication of the signal, and train dispatching is entering the third or "signal indication" stage. (See the section on Train Operation by Signal Indication on p. 951.) Block Systems were developed in England to provide for safe travel by rail. At first the signals were used in much the same way that signals are used to-day by policemen for controlling street traffic. Signalmen known as policemen, stationed along the railroad at hazardous locations (stations, tunnels, etc.) warned the trains by signals of danger ahead. As trains increased in number, signals were next used in an effort to maintain a time interval between trains; protection from rear collisions depending on the continuous maintenance of this time interval between mov ing trains and the use and observance of red flags, lanterns, tor pedoes and fusees for the protection of standing trains ; pro tection from head-on collisions (on single-track lines) depending on the exercise by enginemen and conductors of most intelligent and unceasing vigilance in the observance of rules and written orders and on the exercise of the utmost care by the train dis patcher. As it is not always possible to move trains on schedule time, this method fails to prevent occasional collisions.